In some subfields of Computer Science, usually the order of authors in papers indicate the importance of contributions of authors to a paper. I am currently contemplating the possibility of pursuing a PhD degree. Accordingly, my question is, when applying for PhD positions, do admission committees consider (and if so, how do they evaluate) the order of authors in papers that I have published. Is the number of papers in which I have been the first author an important factor for admission committees?
It depends. Authorship order doesn't always indicate who did the most work or the most important work on a paper in many fields. Some fields are alphabetical. Some fields have the lab leader or the person who won the gran last. Hopefully the admission committee understands the norms of their own field and the field you are coming from (if they are different) to be able to make a good evaluation.
I've never served on a PhD admissions committee, but I understand that they generally will try to determine your contribution to your publications when evaluating your application.